Generate quantization matrix

Question

Hello, how can i generate quantizatinon metrices with diffrent size and quality, is there a function in matlab for this?

Answer 1

Pls explain your context. quantization matrix ... for what ? If you are dealing with JPEG image compression (image blocks + DCT + quantization + huffman coding), the compressor has freedom to use its own quatization matrix - or rather a family of matrices, one for each "quality factor".

Conceptually, one usually want to assign many bits to the low frequency components and few to the high frequencies - but that's about all that can be said in general.

Also, be aware that JPEG compresses luminance and croma separated (and chroma usually subsampled), so one can use different matrices for each.

I believe the standard suggests some typical matrix, eg, including a scaling factor for different qualities. But this is not required at all. Also, you can find (googling!) here many matrices for many cameras and image apps.

Update: From here:

Tuning the quantization tables for best results is something of a black art, and is an active research area. Most existing encoders use simple linear scaling of the example tables given in the JPEG standard, using a single user-specified "quality" setting to determine the scaling multiplier. This works fairly well for midrange qualities (not too far from the sample tables themselves) but is quite nonoptimal at very high or low quality settings.